Currently, the bioenergy is approximately divided into two categories, wherein one is alcohol, and the other is biodiesel oil. The manufacture of bioalcohol utilizes the grain as materials. Recently, the researches gradually turn to generating bioalcohol by microorganisms. There have been many researches pointing out that microorganisms have high potential for generating alcohol. As to the biodiesel oil, it is manufactured from plant materials, discarded edible oil or animal fat. The plant materials mainly are oil grains, such as the soybean, the maize, the rapeseed, the palm, the seed of Jatropha curcushas, the sunflower, etc.; discarded edible oil and animal fat are purified and extracted again to generate biodiesel oil. Both resources of biodiesel oils cannot satisfy the requirements of actual use, and have drawbacks respectively. The oil crop needs a large range of growing land, the crop has seasonal factors, the bioenergy provided by an unit land does not conform to the economic efficiency, there is a problem of competing food with the people, and the extracting procedure is very complex and the cost thereof is high, so the oil crop cannot become the material continuously providing biodiesel oil to replace the petroleum. Discarded edible oil and animal fat have the problems of low quantity, breeding and environmental pollution. Thus, recently the trend is to produce biodiesel oil by the microorganisms. According to researches, the microorganisms can provide 40% of the replaced energy required by the transportation only through occupying 1-3% of the crop growing land, and have rather high potential and advantages.
Utilizing microorganisms to produce oil is not a recent idea. Besides the microalgae and the bacteria, there are oil-generating microorganisms in fungi, most of which are yeast and mould, and some microorganisms simultaneously have the characteristic of generating long-chain saturated fatty acid, monounsaturated fatty acid or polyunsaturated fatty acid. These oil-generating yeasts can produce fatty acid occupied over 40% of biomass and accumulated up to 70% via the limitation and allocation of the medium, which have rather high potential for producing oil. Table 1 shows common oil-generating fungi and the oil quantity produced thereby (Beopoulos, et al., 2009; Gill, Hall, & Ratledge, 1977; Ratledge, 1993, 2002, 2004; Sergeeva Ia, Galanina, Andrianova, & Feofilova, 2008; Zhao, et al., 2010).
TABLE 1FungiLipid % of dry weight (w/w)Aspergillus terreus64Cryptococcus curvatus58Cryptococcus albidus65Candida sp.42Cunninghamella japonica>43.8Lipomyces starkeyi63Penicillium spmulosum64Rhodosporidium toruloides56.5Rhodotorula glutinis72Rhodotorula graminis36Rhizopus arrhizus57Schizochytrium spp.30~50Thraustochytrium spp.30~50Trichosporon pullulans65Yarrowia lipolytica36